Induction heating coil unit for manifold in hot runner mold

ABSTRACT

In an induction heating coil unit for a manifold in a hot runner mold, it is possible to uniformly heat a material over the entire length of a runner. Also, a coil is easily attached to and detached from the manifold. The hot runner mold includes a fixed mold and a movable mold, and a space is provided along a side surface of the manifold on which clamping force applied by the fixed mold and the movable mold does not act. A coil is wound to the side surface along an axial line of a runner of the manifold within the space such that the manifold is induction-heated from the side surface.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application of Ser. No. 09/729,205 filed on Dec. 5,2000, which is a continuation application of PCT InternationalApplication of PCT/JP00/02964 filed on May 10, 2000.

TECHNICAL FIELD

The present invention relates to an induction heating coil unit for amanifold in a hot runner mold.

BACKGROUND ART

In a hot runner mold, it is necessary to maintain material within therunner in a molten condition by heating the runner. Heater heating andinduction heating have been known as methods for heating the runner. Theinduction heating can heat the material to a desired temperature in ashorter time than the heater heating. Further, the induction heating hasthe advantage that it is superior in controllability of temperature andpower consumption is also small.

FIG. 10 is for showing a prior art of the present invention and is aschematic side view of a manifold heated by induction heating.

A manifold 10 has a sprue portion 11 for introducing molten materialsent from an injection cylinder (not shown) into the manifold 10 and arunner portion 12 for distributing the molten material as flown from thesprue portion 11 to nozzles 20. The manifold 10 is disposed within aspace formed between a fixed mold plate 1 of the hot runner mold and aback plate 2 mounted to a rear surface thereof. At a time of injectionmolding, a large mold clamping force acts on the fixed mold plate 1, thenozzles 20 and the back plate 2. For this reason, the manifold 10 issupported by heat-insulating supporting members 16 at a plurality ofportions between the fixed mold plate 1 and the back plate 2 so as toprevent the manifold 10 from being distorted or displaced due to theclamping force.

Coils 15 for induction heating are wound around an outer periphery ofthe manifold 10 at portions at which the manifold is not supported bythe supporting members 16. When voltage is applied to the inductionheating coils 15, the material within the runner is heated at portionswhere the induction heating coils 15 are wound.

In the above-described induction heating method there are the followingdrawbacks.

(1) In order to heat material uniformly, it is preferable to wind thecoils 15 over the entire length of the runner portion 12. However,portions where the coils 15 may be wound will be limited by thesupporting members 16 for supporting the manifold 10. Therefore, thereis a drawback that variations occur in temperature of the moltenmaterial within the runner to result in irregularities in qualities ofinjection-molded articles and in pouring deficiencies.

(2) In case of injection molding of molten metal having a high meltingpoint and exhibiting favorable thermal conductivity, such as magnesium,it will be required to heat the material located at portions whereinduction heating is performed to a temperature that is remarkablyhigher than the melting point thereof. This consequently increases thepossibility of run-out or thermal distortion and also shortens the lifeof the coils themselves.

(3) As one method for solving the above drawback, it is considered toform through holes on the supporting members and to wind the inductionheating coils around the periphery of the manifold 10 through thesethrough holes. However, forming the through holes into the supportingmembers formed of material such as ceramics will result in higher cost.The through holes will further weaken the strength of the supportingmembers.

(4) The respective coils 15 are connected by lead wires each other.These lead wires are connected to an external power supply sourcethrough the back plate 2. A drawback is accordingly presented that thecoils 15 are hard to be detached from the manifold 10 at a time ofperforming exchange, inspection or repair of the manifold 10 and thusworsens the workability.

The present invention has been made in view of these drawbacks, and itis an object thereof to provide an induction heating method for amanifold of a hot runner mold and a coil unit for induction heating withwhich it is possible to uniformly heat material over the entire lengthof a runner without weakening the strength of a supporting member and inwhich the coil may be easily attached to and detached from the manifold.

DESCRIPTION OF THE INVENTION

Clamping force acts onto the manifold 10 in a direction identical to aclamping direction thereof (which is a direction indicated by arrow X inFIG. 10). The inventors of the present invention have completed thepresent invention in view of the fact that no clamping force acts onto aside surface 10 b of the manifold 10 that is parallel to the clampingdirection. In other words, the manifold 10 only needs to be supported bythe supporting members 16 at a surface 10 a that is orthogonal to theclamping direction, and a space in a length direction may be securedover the entire length of the runner portion 12 on the side surface 10b.

More particularly, the present invention relates to an induction heatingmethod for a manifold of a hot runner mold including a fixed mold and amovable mold, the induction heating method comprising the steps of:providing a space along a side surface on which no clamping force isapplied by the fixed mold and the movable mold of the manifold; windinga coil to the side surface along an axial line of a runner of themanifold; and performing induction heating of the manifold from the sidesurface.

According to this method, the material within the manifold may beuniformly heated over the entire length thereof. Attaching and detachingthe coil to and from the manifold will also become easy.

Also, a method may be employed where the coil is wound to extend in aspiral manner from the side surface to a surface orthogonal to theclamping direction, and the manifold is induction-heated from the sidesurface and the surface orthogonal to the claming direction by thisspiral coil.

According to this method, induction heating of the manifold may beperformed not only from the side surface but also from the surfaceorthogonal to the clamping direction so that the temperature of thematerial may be made more uniform. Attaching and detaching the coil toand from the manifold will also become easy.

Furthermore, a method may be employed where the manifold is partitionedinto a plurality of portions to divide each portion into a single regionand the spiral coil is wound for each region to perform inductionheating.

With using spiral coils, it will be possible to easily wind a coilaround an arbitrary portion and to perform induction heating of themanifold from the side surface. It will further be possible to adjusttemperature of the material of each portion to a desired temperature.

An induction heating coil unit according to the present invention is aunit for a manifold of a hot runner mold including a fixed mold and amovable mold, comprising a coil holding body that is provided to beattachable and detachable to and from the manifold and disposed within aspace formed along a side surface on which no clamping force is appliedby the fixed mold and the movable mold of the manifold, and a coil thatis held by the coil holding body and is wound to the side surface alongan axial line of a runner of the manifold, wherein the manifold isheated from the side surface.

With this arrangement, the material may be uniformly heated over theentire length of the runner. The coil may further be easily attached toand detached from the manifold.

Alternatively, the coil holding body may be provided on both of opposingside surfaces of the manifold astride the surface orthogonal to theclamping direction wherein a coil is held by the coil holding body in aspiral manner.

With this arrangement, induction heating of the manifold may beperformed not only from the side surface but also from the surfaceorthogonal to the clamping direction so that the temperature of thematerial may be made more uniform. Attaching and detaching the coils toand from the manifold will also become easy.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1(a) is a schematic plan view of a manifold for explaining theconcept of induction heating method according to the present invention,and

FIG. 1(b) is a view seen from a direction as indicated by arrow A inFIG. 1(a).

FIG. 2 illustrates another embodiment of the induction heating method ofFIG. 1.

FIG. 3 is a perspective view showing a schematic representation of acoil body formed around the manifold according to the embodimentillustrated in FIG. 2.

FIG. 4 illustrates still another embodiment of the induction heatingmethod of FIG. 1.

FIG. 5 is a front view of a coil unit for induction heating according toone embodiment of the present invention.

FIG. 6 is a plan view of the coil unit for induction heating of FIG. 5.

FIG. 7 is a view seen from a direction as indicated by arrows 7—7 of thecoil unit for induction heating of FIG. 5.

FIG. 8(a) illustrates a plan view of another embodiment of a coil unitfor induction heating of the present invention, and

FIG. 8(b) is a side view showing a condition where the coil unit forinduction heating is mounted to the manifold.

FIG. 9 illustrates still another embodiment of a coil unit for inductionheating of the present invention and is a plan view of the coil unit forinduction heating.

FIG. 10 is a side view of a manifold according to the prior art of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferable embodiments of an induction heating method for a manifold ina hot runner mold according to the present invention will be explainedbelow with reference to the drawings. It should be noted that portionsand members that are identical to those of the manifold as illustratedin FIG. 10 are marked with identical reference numerals, and detailedexplanations thereof will be omitted.

FIG. 1 is a schematic view of a manifold for explaining the concept ofan induction heating method according to the present invention, whereinFIG. 1(a) is a plan view thereof, and FIG. 1(b) is a view seen from adirection as indicated by arrow A in FIG. 1(a).

Clamping force that is applied when a movable mold plate (not shown) ispressed against a fixed mold plate 1 acts in a direction as indicated byarrow X in FIG. 1. A surface 10 a of a manifold 10 that is orthogonal tothe direction indicated by arrow X is supported by heat-resistantsupporting members 16 at predetermined portions. A space is securedbetween the fixed mold plate 1 and a back plate 2 on the side surface 10b side of the manifold 10 that is parallel to the direction indicated byarrow X. A (oil 17 is wound within this space along the side surface 10b). It is alternatively possible to preliminarily form a coil unit bywinding the coil 17 along the side surface 10 b of the manifold 10 andto mount this coil unit to a periphery of the manifold 10 whenassembling the manifold 10.

As described above, there is no obstacle such as the supporting members16 on the side surface lob of the manifold 10. Thus, the coil 17 may beeasily wound around the manifold 10. By applying voltage to the coil 17,induction heating may be performed along the entire length of a runnerportion 12 of the manifold 10 and thus to uniformly heat material withinthe runner.

FIG. 2 illustrates an embodiment of the induction heating method of FIG.1. Both ends of the manifold 10 in longitudinal direction may be fixedto the back plate 2 through fixing members 22, 22. In this embodiment, acoil 18 is wound in a spiral manner to extend from the side surface 10 bof the manifold 10 to the surface 10 a while avoiding the fixing members22, 22. The coil unit thus formed assumes a shape of a saddle opened atits central portion, as illustrated in FIG. 3. The coil body having sucha shape as illustrated in FIG. 3 may be easily attached to the manifold10 from the surface 10 a on the back plate 2 side.

Even in this embodiment, when voltage is applied to the coil 18, therunner portion 12 of the manifold 10 may be similarly heated over theentire length and the material contained therein may be uniformlyheated.

FIG. 4 illustrates still another embodiment of the induction heatingmethod of FIG. 1. In this embodiment, the manifold 10 is partitionedinto a plurality of regions. Coils 19 are wound to extend from the sidesurface 10 b to the surface 10 a in respective regions. In theillustrated example, the manifold 10 is divided into three portions ofboth end portions supported by the supporting members 16 and a centralportion having a sprue portion 11. The number of division is not limitedto three but may also be two or not less than four. By attaching thecoils 19 to the respectively divided regions in this manner, themanifold 10 may be heated for each desired region. It is furtherpossible to uniformly heat the material over the entire length of therunner portion 12 by disposing a predetermined number of coil unitscomprised by wound coils 19 in accordance with the length of themanifold 10, irrespective of the dimension of the manifold 10 beingeither long or short. In this case, it is desirable to connectrespective coils 19 to be mutually attachable and detachable by means ofconnectors.

One embodiment of a coil unit for induction heating according to thepresent invention will now be explained in details with reference toFIGS. 5 to 7.

FIG. 5 is a front view of a coil unit for induction heating according toone embodiment of the present invention, FIG. 6 is a plan view of thecoil unit for induction heating of FIG. 5, and FIG. 7 is a view seenfrom a direction as indicated by arrows 7—7 of the coil unit forinduction heating of FIG. 5.

A coil unit for induction heating 30 comprises a hollow andsaddle-shaped coil holding body 32 that is freely attachable/detachableto and from the manifold 10, a coil 33 held by the coil holding body 32,and a cover 36 for covering an exterior of the coil holding body 32.

The coil holding body 32 is formed of non-conductive material withsuperior heat-resistant properties, for instance, ceramics. On a surfacethereof, a helically continuous groove 32 a is formed along an outerconfiguration of the coil holding body 32. The coil, 33 is fitted intothis groove 32 a while being helically wound and is held thereat. Thecoil 33 fitted into the groove 32 a may be fixed to the coil holdingbody 32 through arbitrary and suitable adhesive or the like exhibitingsuperior heat-resistant properties. Both ends of the coil 33 are ledoutside the coil unit for induction heating 30 by a terminal handlingmember 35 provided on one side of the coil holding body 32.

The coil holding body 32 is further provided with engaging pawls 34 onboth ends of its opening portion for engaging with corner portions ofthe manifold 10. The engaging pawls 34 are formed to assume taperedshapes when seen from the side surface for enabling easy attaching anddetaching to and from the manifold 10 of the coil unit for inductionheating 30.

One or a plurality of the coil units for induction heating 30 of theabove-described arrangement may be mounted in a longitudinal directionof the manifold 10. In a case that the plurality of the coil units forinduction heating 30 are attached in the longitudinal direction, it ispreferable to connect the coils 33 of respective coil units forinduction heating 30 by connectors 40. The connector 40 may has anyconventional arrangement as far as both ends of the coils 33 and leadwires 39 may be easily connected.

The connector 40 in this embodiment comprises a case 41 whose interioris formed with two chambers 43 a, 43 b by an insulating partition 42,and conductive holding members 44 a, 44 b that are respectively insertedinto the chambers 43 a, 43 b of the case 41. The holding members 44 a,44 b are respectively formed with grooves 46 a, 46 b into which bothends of the coil 33 and the lead wire 39 are fitted. The case 41 isfurther formed in a structure that is vertically separable into twoparts. One of the parts serves as a holding member for fixing both endsof the coil 33 and the lead wires 39 by pinching, and is furtherprovided to enable disassembly and assembly through bolts 48 formounting the connector 40 to the back plate 2 (see FIG. 10). Thus, byloosening the bolts 48, the case 41 of the separable arrangement isloosened for enabling attaching and detaching of both ends of the coil33 and the lead wires 39. Since the holding members 44 a, 44 b areformed of metal exhibiting superior conductivity such as iron, steel oraluminum, both ends of the coil 33 and the lead wires 39 may beconnected in an easy and reliable manner by simply fitting both ends ofthe coil 33 and the lead wires 39 to the grooves 46 a, 46 b,respectively, and fastening the bolts 48.

In the coil unit for induction heating 30 to be mounted around the sprueportion 11, it is preferable to form a fit-mounting portion 50surrounding the sprue portion 11. With the fit-mounting portion 50, thecoil unit for induction heating 30 can accurately be positioned abovethe manifold 10. By winding a coil (not shown) around the fit-mountingportion 50, material in the sprue portion 11 may also be heated. Itshould be noted that the sprue portion 11 of the manifold 10 bepreferably of straight shape without any projections such as flanges inview of attaching and detaching of the coil unit for induction heating30 provided with the fit-mounting portion 50, Further, it is preferablethat the thickness of the sprue portion 11 is made as thin as possiblefor realizing effective heating through induction heating.

When the coil unit for induction heating 30 of the above-describedarrangement is mounted to the manifold 10 and current is supplied to thecoil 33 through the lead wires 39 and the connector 40, the manifold 10is induction-heated from the side surface 10 b side so that the materialwithin the runner 12 (see FIG. 10) is uniformly heated.

Another embodiment of the coil unit for induction heating according tothe present invention will now be explained with reference to FIG. 8.

As illustrated in FIG. 8(a), a coil unit for induction heating 50 of theillustrated embodiment comprises a bag-like heat-resistant cloth 51 thatis wound around the manifold 10 and mounted thereto, a spiral coil 53mounted to an inner side of the bag-like heat-resistant cloth 51, andstring-like tying portions 52 provided on both ends of theheat-resistant cloth 51.

The heat-resistant cloth 51 is comprised by weaving heat-resistantfibers such as alumina fibers or aluminosilicate fibers in a bag-likemanner. It is alternatively possible to form the cloth 51 in a bag-likemanner by adhering or sewing a plurality of heat-resistant clothstogether. An opening 55 may be formed on a predetermined portion of theheat-resistant cloth 51 which allows insertion of the sprue 11 or thelike, as illustrated in FIG. 8(b).

The coil for induction heating 53 is disposed inside the bag-likeheat-resistant cloth 51 in a spiral manner. The coil for inductionheating 53 is preliminarily wound in a spiral manner such that adjacentwires do not contact each other. This coil for induction heating 53 issewn to the heat-resistant cloth 51 within the bag-like heat-resistantcloth 51 by a heat-resistant member such as one of the above-listedheat-resistant fiber or the like.

Both ends of the coil for induction heating 53 project outside thebag-like heat-resistant cloth 51.

The string-like tying portions 52 may be formed from a part of theheat-resistant cloth 51, and it is alternatively possible to sewseparately formed tying portions 52 to both ends of the heat-resistantcloth 51 by using one of the above-listed heat-resistant fiber or thelike.

The thus arranged coil unit for induction heating 50 is bent to suit theouter shape of mounting portions of the manifold 10, as illustrated inFIG. 8(b). The tying portions 52, 52 on both ends of the heat-resistantcloth 51 are tied astride the manifold 10.

In this manner, the coil for induction heating 53 may be mounted to themanifold 10 together with the heat-resistant cloth 51.

Thereafter, both ends of the coil 53 projecting outside the coil forinduction heating 53 are connected to lead wires (not shown) that areconnected to an external power source.

The tying portions are not limited to those of the above-describedembodiment.

It is, for instance, possible to provide male snaps 57 on both ends ofthe heat-resistant cloth 51 and to provide female snaps 59 on both endsof the string-like tying members 58 formed as separate bodies from theheat-resistant cloth 51, as shown in FIG. 9. By fitting the male snaps57 and the female snaps 59 together, both ends of the heat-resistantcloth 51 may be tied by the tying members 58.

Though not shown in the drawings, both ends of the heat-resistant clothmay be tied by heat-resistant wires as another embodiment.

According to these embodiments, attaching and detaching the coil unitfor induction heating 50 to and from the manifold 10 may be performed ina still simpler manner, and such embodiments are also advantaged in viewof costs.

According to the present invention, a coil for induction heating iswound to a side surface on which a clamping force of a manifold does notact along an axial direction of a runner, the coil may be wound over theentire length of the runner to make the temperature of molten materialcontained in the runner uniform, and it is accordingly possible toprevent irregularities in qualities of injection-molded articles andoccurrence of pouring deficiencies.

Since the material may be uniformly heated, it will no more be necessaryto partially perform heating at a temperature that is remarkably higherthan a melting point when performing injection molding of molten metalhaving a high melting point and exhibiting favorable thermalconductivity such as magnesium, and to thereby reduce the danger ofrun-out or thermal distortion or the like. The life of a coil itselfwill not be shortened, either.

Since a coil may be wound irrespective of supporting members, thestrength of the supporting members will not be weakened.

Coils may be easily attached to and detached from the manifold and thusexhibits superior workability.

Industrial Applicability

The present invention is widely applicable to molds in a hot runnerinjection molding not only for resin but also for metals such asmagnesium alloy, aluminum alloy or zinc alloy.

What is claimed is:
 1. An induction heating coil unit for a manifold ina hot runner mold including a fixed mold and a movable mold, saidmanifold having a runner with side surfaces where no clamping force isapplied by the fixed and movable molds, said coil unit comprising: acoil holding body having means to be attachable to and detachable fromthe runner of the manifold and to be disposed along the side surfaces ofthe manifold, and a wound coil held by the coil holding body and havingfour coil sections extending continuously as one unit, at least two ofthe four coil sections facing each other and rest of the coil sectionsbeing disposed between the two coil sections facing each other to allowthe four coil sections to be disposed along the side surfaces of therunner of the manifold to heat the manifold from the side surfaces. 2.The induction heating coil unit for a manifold of a hot runner mold asrecited in claim 1, wherein the coil holding body is provided with twoside surfaces facing each other and one side surface between the twoside surfaces to face three sides of the manifold, said coil extendingin a spiral form on the three side surfaces and being held by the coilholding body.
 3. The induction heating coil unit for a manifold of a hotrunner mold as recited in claim 1, wherein the coil holding body is aheat-resistant cloth.
 4. The induction heating coil unit for a manifoldof a hot runner mold as recited in claim 3, wherein the heat-resistantcloth includes tying portions on two ends, said heat-resistant clothbeing adapted to be mounted on the manifold and attached thereto bytying the tying portions astride the manifold.
 5. The induction heatingcoil unit for a manifold of a hot runner mold as recited in claim 1,wherein said coil holding body has four side surfaces in a form of aloop extending in a direction perpendicular to a clamping forceapplication direction, said coil being wound spirally on the four sidesurfaces of the coil holding body.
 6. The induction heating coil unitfor a manifold of a hot runner mold as recited in claim 1, wherein saidrest of the coil sections are disposed on one side between the two coilsections facing each other so that the coil sections are located atthree sides.